Schema for describing and exploiting Solar Resource Knowledge. Units are expressed as string. Examples: kWh/m2, W/(m2.sr), W.m-2.sr-1, rad, ° denotes the absence of a value. Usually equals -99 or -999 for the sake of the simplicity, latitude is in decimal degrees for the sake of the simplicity, longitude is in decimal degree for the sake of the simplicity, elevation is in m for the sake of the simplicity, date and time are expressed in UT, such as YYYY-MM-DDThh:mm:ss. Using seconds permit to describe accurately the True Solar Time in UT. duration of a measurement or aggregation Describes a single observation of radiation. Date is the instant of observation, value is the count (measure), accuracy denotes uncertainty and reliability denotes the confidence in the observation. Note that usually date denotes the end of the period of the measurement (summarization). For example, if the period is 1 h, dateTime equals to 2008-25-01T18:43:26 means that the observation was made during this day from 17:43:27 to 18:43:26. It happens that several observers do not follow that rule and that the time may be, say the middle of the hour. The "offsetInstant" has been created to manage such case. It is expressed in percent. 100 means that it is the end of the summarization, 50 the middle, 0 the beginning etc.